1. Field of the Invention
This invention relates to a method of carbonizing a substance comprising cellulose and more particularly, to a method of carbonizing cellulose-containing waste products with an alkali metal aluminate which has been dissolved in sewage sludge containing, typically, from 4-7% of solid material, e.g. faeces.
2. Description of the Prior Art
As is well known, the United States is a conglomerate of municipalities, the vast majority of which have populations below 100,000. These municipalities produce vast amounts of waste material which, in turn, dictates massive landfill or incineration programs. However, in most municipalities there is typically not enough waste to make it profitable to build electric power or chemical plants, adjacent to the municipal incinerator or sewage plant, to recover or recycle this waste material.
"Municipal solid waste" as that term is used herein will be understood as referring to raw refuse such as domestic rubbish and garbage of the type which is discarded within municipalities and handled by collection and disposal systems. It will be understood that although the term suggests only such waste as is collected by a municipality and/or treated by a municipality, the present invention is applicable to and includes such solid waste material whether or not a municipality has been involved in its collection or treatment.
Municipal solid waste although variable from time to time and from place to place has been analyzed to be of the following average composition:
______________________________________ Paper, cardboard, etc. 50-70% Miscellaneous organics, such as plastics, wood, food products, etc. 10-20% Nonmetallic materials such as metallic oxides, glass earth ceramics, etc. 10-20% Ferrous metals such as iron and steel 5-10% Nonferrous metals such as copper, aluminum, zinc, etc. 0.2-1% ______________________________________
A technique whereby cellulose-containing materials can be completely carbonized or charred without leaving a residue, i.e., without incineration and formation of an ash, is disclosed in my U.S. Pat. No. 3,961,025 which issued on June 1, 1976, which patent is hereby incorporated by reference as if more fully set forth herein.
As disclosed in the above - referenced patent, my priorly patented method includes combining the cellulose-containing waste substance with an alkali metal aluminate to form a carbonizing mixture. The carbonizing mixture is then heated to carbonize the substance.
This process which operates in a closed system and is therefore pollution free, yields carbon/carbon dioxide and flammable distillation gases. Further, the alkali metal aluminate can be recovered and re-used.
However, solid waste per se is not the only problem facing today's small -- municipalities. We must also consider the problem of sewage sludge. Because within the next decade, the amount of sludge that accumulates in the course of a year will have more than doubled. Only recently have we come to realise the danger that can arise if this sludge is dumped without treatment. For example, we now know that sewage sludge is a carrier of hepatitis viruses, salmonellae (which are carried inland from coastal dumps by seagulls, for example), benzopyrone in aerosol form and other polycyclic aromatic substances which are carcinogenic.
Even when sludge is disposed of in an approved manner, most of these harmful substances remain intact and represent a latent danger. Anthrax virus, for example, has been known to survive in total isolation for decades. Further, when fermentation starts, the interior of a refuse tip resembles a chemical factory because of the lack of air or oxygen in the tip. This danger does not even come to light until vegetation, small trees and the like, are planted on the man-made hillock. This vegetation soon withers and dies because its roots are unable to find nutrients, striking nothing but methane and sulphur dioxide.
I consider raw sewage sludge to have the following typical chemical composition:
______________________________________ Total dry solids 4.0% Volatile solids 59.0% Protein 20.0% Cellulose 10.0% Nitrogen 2.5% Phosphorus (P.sub.2 O.sub.5) 1.6% Potash (K.sub.2 O) 0.4% Iron (not as sulfide) 2.5% ______________________________________
The problem, then, is to devise a pollution-free process for safely disposing of both municipal solid waste and sewage sludge.